Third Generation (3G) wireless communications systems such as the Universal Mobile Telecommunications System (UMTS) operate within a regulated portion of the RF spectrum. FIG. 1 shows the current allocation of spectrum to 3G wireless systems. There are three separate bands of spectrum between 1900-1980 MHz, 2010-2025 MHz and 2110-2170 MHz. Together these are known as the 3G core band. Different telecoms operators are granted different parts of the spectrum within these bands for their uplink and downlink channels. Uplink and downlink channels occupy separate frequency bands and a duplex pair of uplink and downlink channels is offset by a fixed frequency of 190 MHz.
Increasing demand for services in this band has prompted manufacturers, operators and regulators to investigate the possibility of using additional spectrum outside of that originally allocated. One possibility for additional 3G spectrum which is currently being considered is the band from 2.5 to 2.69 GHz; this is being referred to as the 3G Extension Band. There are various ways in which the additional spectrum can be used. The Third Generation Partnership Project (3GPP) has proposed a range of possible scenarios for using the additional spectrum. In some of these scenarios, the extension band is wholly or primarily used for additional downlink channels to support higher bandwidth delivery to terminals.
The applicant has identified a problem which can occur when the additional spectrum is used in this way.
The present invention seeks to provide a way of minimising or overcoming this problem.